Electric snap switch



Jan. 18, 1949. A. M. MacFARLAND 2,459,66i

ELECTRIC SNAP SWITCH Filed July 11, 1945 3 Sheets-Sheet 1 Z 3 f3 16 a IN! 'EN TOR.

I 4290 1;]? ZKac/Zr/azd 'TLUL M w Jan. 18, 1949. A. M. MacFARLAND 2,459,661

ELECTRIC SNAP SWITCH Filed July 11, 1945 3 Sheets-Sheet 2 1949- A. M. M FARLAND 2,459,661

ELECTRIC SNAP SWITCH Filed July 11, 1945 z Sheets-Sheet 3 0 I Q Q l A49 4/6 50 IN VEN TOR.

Patented Jan. 18, 1949 ELECTRIC SNAP SWITCH Allison M. MacFarland, Freeport, 111., assignor to W. T. Neiman, Freeport, Ill.

Application July 11, 1945, Serial No. 604,382 16 Claims.. (Cl. 200-67) This invention relates to improvements in electric snap switches. More particularly, the invention pertains to snap switches of the type wherein the snap action results from the application of forces applied by a leaf spring system having an unstable dead center position.

The object of the invention is to provide a snap switch of improved construction and operating characteristics. The device is extremely simple and is adaptable for operation by a wide variety of actuating impulses and over a broad range of capacities.

In the accompanying drawings,

Fig. 1 is a cross-sectional elevation of one form of a complete snap switch embodying the invention;

Fig. 2 is a plan view of the interior of the switch of Fig. 1;

Fig. 3 is a plan view of the actuating leaf spring of the switch of Figs. 1 and 2;

Fig. 4 is a perspective view of the contact bar of the switch of the Figs. 1 and 2;

Fig. 5 is a diagrammatic view of the essential operating elements of the switch;

Fig. 8 is a cross-sectional view of the operating elements of a switch having a modified form of leaf spring;

Fig. 7 is a plan view of the interior of a snap switch embodying an alternative structure;

Fig. 8 is a cross-sectional view of the" operating elements only of the switch of Fig. 7

Fig. 9 is a cross-sectional elevation of a double pole snap switch embodying the invention; I

Fig. 10 is a cross-sectional view of the operating elements only of a snap switch having a different form of actuating leaf spring; and

Fig. 11 is a plan view of the leaf spring of the switch of Fig. 10.

Briefly, the switch consists essentially of a contact bar anchored at one end and having a free end which moves between stops, one or both of which may be electrical contacts, and leaf spring actuating means. The leaf spring comprises one or more tension legs or strips anchored at one'end and one or more compression legs or strips approximately parallel, in plan, to the 'tensionstrips and connected thereto at their ends remote from the tension strip anchorages. The free end or ends of the compression strip or strips bear against a thrust seat on the contact bar in 2 A preferred embodiment of the invention is illustrated in Figs. 1 to 4 of the drawings. The

a direction calculated to place the contact bar in tension from the point of anchorage. The switch is actuated by the application of a force which shifts the position of the butt end of the leaf spring.

switch mechanism is mounted upon a base i of Bakelite or other suitable structural insulating material which, together with cover 2, forms a housing for the switch. An electrical contact 3 is fixed upon base I and is electrically connected to switch terminal 4 by suitable fastening means such as rivets or screws 5 and 6 threaded into a sleeve insert in the base of the switch. A contact bar 1 is anchored at one end to base I by means of an anchor pin 8 which is rigidly supported in base i and electrically connected to switch terminal 9 by suitable means such asthat illustrated. The free end of contact bar I is provided with an electrical contact block III which is adapted to engage contact 3 to close the switch circuit.

Contact bar 'I'is actuated and its positlon controlled by. the forces exerted by a leaf spring system. In the particular switch illustrated in Figs. 1 and 2, this leaf spring i i is in the form of a three-tyned fork separately illustrated undeformed in Fig. 3. The ends of the outer tynes or strips i2 of the spring are fastened to base I of the switch by screws 13. It may be noted that the operation of the switch requires only that these members be anchored to the switch base, the fixed mounting being illustrated because of the greater convenience in assembly with this arrangement. The end of inner tyne or spring strip I4 is stepped in a notch or thrust seat l5 provided to receive it at a point near the free end of contact bar I. This seat faces the anchored end of the contact bar and receives the thrust of compression spring strip I 4 outwardly from the anchorage at 8. The length of spring strip l4 and the location of the anchorages of strips I2 are such that strip i4 must be-bowed in orderto insert its end in seat I5. In assembling the switch, the center leg I4 is depressed, and, being under compressive stress in this position, the butt end l6 of the leaf spring is urged upwardly against the switch actuating plunger ll.

In order to accommodate the bowed middle I 7 These branches lie between the middle and outer 1 legs of theleaf spring in the switch assembly.

Unless the nature of the anchorage is such that movement of the contact bar between the fixed contacts or stop and contact is unimpeded the spring system and the character designates a strip which'is under compression. The corresponding elements of the switch of Figs. 1 and 2 are strips l2 and I4, respectively. The character P designates the arrow which represents the downward force applied by means of plunger II. Other elements of the diagram are readily related to the mechanical counterparts in the switch structure of Figs. 1 and 2 by the-similarity of numeral designationa The switch mechanism diagrammatically illustrated in Fig. 5 is one in which the internal circuit is normally open. The free contact end in of contact bar 'I' rests upon astop formed by a portion of insulating base I'. With the spring system anchored at I2 and the free or butt end It of the spring H maintained at a given level by the force P, a thrust or force having both horizontal and vertical components is exerted at seat i! of the contact bar I. The portion'of the contact bar between step I! and theanchorage I is under tension, this condition being maintained for all positions of this element.

Analysis of. the effective forces of the spring system shows that the vertical component of force applied by thespring to the contact bar at seat I! may be altered in magnitude and reversed in direction by varying the magnitude of force P and thus the position of .they buttend it of the spring. As this force is increased, the butt end It of the leaf spring is depressed, the magnitude of the stresses in tension strip T and compression strip C are increased and the-direction of the resultant force applied to the contact bar at'seat i5 changes. Although it is theoretically possible to apply a force at P which will result in a horizontal resultant force step IS without vertical components, this being the condition for placing the switch mechanism in dead center position, the system is extremely unstable under such conditions and the dead center status is impossible to attain in practise. Actually, as the force P is increased, the downward component of force which holdsthe free or contact end of contact bar I against the insulating stop I abruptly changes to an upward component which starts the contact end ill of the bar in upward motion. This initial displacement moves the point of application of the forceof the spring system at seat I! upwardly with the result that the upward component of force is increased and the motion of the bar greatly accelerated. The result is a snap action in brin s ing thecontact end ll of bar linto engagement with contact 3-. Similarly, diminution of the force P permits'the free end of the leaf spring to move upwardly, opening the-switch with a snap action. Special attention is directed to the nature and effect of a lateral as well as a longitudinal force exerted by the compression strip C of the spring system. This leg of the leaf spring. bei g bowed.

plunger 32 depresses the free end of spring 20 and and depressed below the general level of tension strip '1, exerts an upward force upon the contact bar due to the deformation of this spring strip at the point of junction with the butt end I. of the spring ii. Thus, the compression strip becomes a floating cantilever. This force, which is only one element of the resultant force applied to the thrust seat, has the effect of lowering the dead center position of the contact bar and serves to accentuate the snap action. The latter effect is the result of an increased deformation of compression.='s'trip C as butt end I6 is depressed, the end ofethe strip in the thrust seat being below the center of rotation of the opposite end of the strip and thus approached as the butt end of the spring is depressed.

.Theextent of travel of plunger i1 and the magnitude of the force which must be applied to this plunger in order to operate the switch depends, in part, upon the location of the point of application of this force. In Fig. 1 the plunger engages the leaf spring near the free end. This force may be applied either at the butt end I of the spring or may be applied at any point along the length of the outer or tension strips l2. Downward pressure applied, for example, midway between the anchorage l3 and the Junction of the inner leg M with the outer legs l2 has the effect of lowering the entire spring assembly at the same time as the free end is depressed. A greater force is required with less displacement and the lowering of the entire spring assembly under the influence of the depressing force appears to improve the snap action.

On the other hand, a switch to be operated with a smaller force and greater plunger travel may be provided by extending the free end of the spring in the manner illustrated in Fig. 6. In this form of the device, the flexible extension I! of the leaf spring absorbs a portion of the motion of plunger 20. This figure also illustrates an alternative form of contact bar '62 having a depressed central portion 63 for the accommodation of spring strip 64.

An alternative form of switch structure is illustrated in Figs. '7 and 8. This device operates in the same manner as that hereinbefore described, the difference in structure residing in the manner in which the forces of the leaf spring are applied to the contact bar in the actuation of the switch. An insulating base 2|. forms a part of the switch housing and an electrical contact 22 is mounted on the base. A contact bar 23 is anchored or aflixed by means of screw 24 to base 2! and carries a contact 25 at its free end which is adapted to engage electrical contact 22 to close the switch circuit. A three-tyned leaf spring 28, similar to spring ii of Figs. 1 to 3, is employed. However, in the modified structure of Figs. 7 and 8, the end of the middle leg 21 is flxed and this spring strip serves as the tension member while the outer strips 28, which are the compression elements of the spring system, are stepped in thrust seats 29 of contact bar 23. The end of tension strip 21 may be conveniently mounted by means of an insulating support 30 and,rivet or belt 2i.

As inthe case of the switch'hereinbefore described, a downward .force applied by means of causes the free end of contact bar 22 to move upwardly with a snap action. Removal of this force upon the plunger again opens the switch circuit as the electrical contacts 22 and 25 disengage with a snap action.

A double pole switch is illustrated in Fig. 9. An

s electrical contact SI is mounted in base 84 and electrically connected to switch terminal I! by means of screws I6 and a suitable sleeve insert into which the screws are threaded. A second electrical contact 3'! is similarly mounted and connected to a second switch terminal, not shown. Contact bar 38, similar to that illustrated in Fig. 4, is anchored or aflixed to base It and electrically connected to a third switch terminal 39 by means of screws 40 and a suitable sleeve insert. 1

A leaf spring 4|, similar to that described in connection with Figs. 1 to 3, is mounted upon base 84 by means of screws 42. The compression leg 48 of this spring is stepped in thrust seat It in the manner previously described. An electrical contact 45 is provided at the free end of contact bar 18 to engage either electrical contact 33 or contact 31. The switch is operated by means of plunger 48 extending through cover 41.

In the operation of this switch, either one or the other of two switch circuits is closed. Actuation may be controlled entirely by means of plunger II or the leaf spring and electrical contacts may be so arranged that when the free end of the spring is depressed beyond the level at which the contact bar moves upwardlv to clo e the circu t of contact a and then released, the contact bar does not return to its original position, but remains in engagement with contact 33. A second plunger ll may then be employed to shift the spring and cause the switch to snap back to its original position.

The modified switch mechanism illustrated in Fig. it) employs a leaf spring having only a sin le tension leg 48 and a single compression leg 49. These two elements of the spring are securely riveted together at 50. The upper strip 48, which functions as the'tension member, is mounted in ilxed relation to the base 52 of the switch by suitable means such as insulating strip It extending from electrical contact 54. The lower spring strip 49 is stepped in thrust seat I! of contact bar Bl. This contact bar is mounted at one end to base 52 by means of screw 51 and is free to move between stops formed by base 52 and electrical contact 54.

This switch mechanism operates exactly in the same manner as hereinbefore described. the ar-' ticular advantage of the modified form of spring being that the switch structure may be con siderably narrower.

It will be appreciated that the form of the several elements of the switch herein described may be altered without departing from the mode of operation of the mechanism. Alternative forms of certain of these elements disclosed in the several embodiments illustrated may be interchanged without aifecting the operation of the resulting device.

I claim:

1. A snap switch comprising a switch base, a pair of fixed stops at least one of which is an electrical contact mounted in said base, an electrically conductive contact bar anchored atone end to said base and having a free end movable between said stops and a thrust seat arranged near said free end and facing the anchored end thereof, spring means for actuating said contact bar, said spring means comprising substantially parallel leaf spring separate compression and tension strips rigidly joined together at one end thereof, the free end of a tension strip being anchored on said base and the free end of a compression strip being stepped in the thrust seat upon said contact bar whereby vertical and longitudinal components of force are applied to said contact bar at the thrust seat, and means responsive to external manipulation for depressing the Joined ends of said spring strips to actuate the switch.

2. A snap switch comprising a switch base. a pair of flxed stops at least one ,of which is an electrical contact mounted in said base, an electrically conductive contact bar anchored at one end to said base and having a free end movable between said stops and a thrust seat arranged near said free end and facing the anchored end thereof. spring means for actuating said contact bar, said spring means comprising substantially parallel leaf spring separate compression and tension strips rigidly joined together atone end thereof, the free end of a tension strip being anchored on said base and the free end of a compression strip being stepped in the thrust seat upon said contact bar, said compression strip being bowed and depressed below the general level of the tension strip, the arrangement being such that said compression strip exerts force components both longitudinal and vertical with respect to said contact bar at said thrust seat, and means responsive to external manipulation for depressing the joined ends of said spring strips to actuate the switch.

3. A snap switch in accordance with claim 2 wherein the compression spring strip is bowed sufficiently to bring a ortion of the strip below a line extending from the thrust seat to the point of anchorage of the contact bar.

4. A snap switch in accordance with claim 2 wherein the compression spring strip is bowed sufilciently to bring a portion of the strip below a line extending from the thrust seat to the point of anchorage of the contact bar, said contact bar being formed to permit operation of said compression strip without engagement therewith except at the thrust seat.

. 5. A snap switch in accordance. with claim 2 wherein the compression spring strip is bowed sufficiently to bring a portion of the strip below a line extending from the thrust seat to the point of anchorage of the contact bar, said contact bar being bifurcated at the thrust seat to form an opening adapted to accommodate the compression strip.

6. A snap switch in accordance with claim 2 wherein the compression spring strip is bowed sufliciently to bring a portion of the strip below a, line extending from the thrust seat to the point of anchorage of the contact bar, said contact bar having a depressed portion inwardly adjacent said thrust seat adapted to accommodate the compression strip.

7. A snap switch comprising a switch base, a pair of fixed stops at least one of which is an electrical contact mounted in said base, an electrically conductive contact bar anchored at one end to said base and having a free end movable between said stops and a thrust seat arranged near said free end and facing the anchored end thereof, spring means for actuating said contact that said compression strip exerts force .components both longitudinal and lateral with respect to said contact bar at said thrust seat, and means responsive to external manipulation i'or depressing the joined ends of said spring strips to actuate the switch. said stops being arranged to limit upward movement of the free end of said contact bar to a point at which the thrust seat is below the level of the anchored end of the tension strip.

8. A snap switch comprising a switch base, a pair of ilxed stops at least one: of which is an electrical contact mounted in said base, an electrically conductive contact bar anchored at one end to said base and having a free end movable between said stops and a thrust seat arrangement near said free end and facing the anchored end thereof, spring means for actuating said contact bar, said spring means comprising an integral leaf spring having three spring strips extending in substantial parallelism from the butt end of said leaf spring, the ends of the outer spring strips being anchored to said base, the inner spring strip being bowed and depressed below the general level of said outer spring strips and stepped in the thrust seat upon said contact bar whereby vertical and longitudinal components of force are applied to said contact bar at the thrust seat, and means responsive to external manipulation for depress ing the butt end of said leaf spring to actuate the switch.

9. A snap switch comprising a switch base, a pair of fixed stops at leastone of which is an electrical contact mounted in said base, an electrically conductive contact bar anchored at one end to said base and having a free end movable between said stops and a thrust seat arranged near said free end and facing the anchored end thereof, spring means for actuating said contact bar, said spring means comprising an integral leaf spring having three spring strips extending in substantial parallelism from the butt end of said leaf spring, the ends of the outer spring strips being anchored to said base, the inner spring strip being bowed and depressed below the general level of said outer spring strips and stepped in the thrustseat upon said contact bar whereby vertical and longitudinal components offorce are applied to said contact bar at the thrust seat, and means responsive to external manipulation i'or depressing the butt end of said leaf spring to actuate the switch, said stops being arranged to limit upward movement of the free end of said contact bar to a point at which the thrust seat is below the level of the anchored ends of the outer spring strips.

10. A snap switch comprising a switch base, a

'pair of fixed stops at least one of which is an electrical contact mounted in said base, an electrically conductive contact bar anchored'at one end to said base and having a freeend movable between said stops-and a thrust seat arranged ,near said free end and facing the anchored endthereof,

spring means for actuating said contact bar, said 1 spring means comprising a unitary leafspring arranged generally above said contact bar and having three spring strips extending in substantion of the contact bar inwardly adjacent said thrust seat being divided to receive said compression strip, and means responsive to external manipulation for depressing the joined ends of said spring strips to actuate the switch.

11. A snap switch in accordance with claim 2' and including a flexible extension of said spring means from the Joined ends of said spring strips,

said means for depressing the Joined ends of the spring strips being applied near the free end of said flexible extension.

12. A snap switch comprising a switch base, a pair of fixed stops at least one of which is an electrical contact mounted in said base, an elec-' tricaliy conductive contact bar anchored at one end to said base'and having a free end movable between said stops and a thrust seat arranged near said free endand facing the anchored end thereof, spring means for actuating said contact bar, said spring means comprising substantially parallel leaf spring separate compression and tension strips rigidly joined togetherat one end thereof, the, free end of a tension strip being anchored on said base and the free end of a compresslon strip being stepped in the thrust seatupon said contact bar, said compression strip being bowed in compression,-the arrangement being such that said compression strip exerts a force having both longitudinal and vertical components with respect to said contact bar at said thrust seat, and a plunger arranged for external manipulation and engaging the joined ends of said spring strips to alter the level thereof and thus actuate the switch, said fixed stop being so arranged that the position of said contact bar, is

stable at both extreme. positions thereof without continued manipulation of said plunger. 13. A snap switch comprising a housing in- I eluding a base and a cover, a first electrical contact mounted in said base, a second electrical contact mounted upon said base above and in spaced relation to said first contact, an elec-,

trically conductive contact bar anchored at one end upon said base andhaving a free end movable between said contacts, said contact bar having a thrust seat arranged thereon near its free end and facing its anchored end, said contact bar being bifurcated at the thrust seat to form a divided portion inwardly from said thrust seat, spring means for actuating said contact bar, said spring means comprising a unitaryleaf spring arranged generally above said contact bar and having three spring strips extending in substantial parallelism from the butt end of said leaf spring, the ends .of the outer spring strips being mounted upon said base, the inner spring strip being stepped in the thrust seat upon said contact bar and bowed in compression and arranged as operate between the branches of the divided portion of the contact bar, a plunger extending through the cover of said housing and engaging the butt end of said leaf spring, a second plunger extending through .said base and between the tial parallelism from the butt end of said leaf spring, the ends of the outer spring strips being line extending from the thrust seat to the point 01 anchorageoi the contactbarand being stepped in the thrust seat upon said contact bar, the pmbranches of the divided portion of said contact bar and engaging the butt end of said leaf spring, and means for electrically connecting said contacts and said contact bar to external switch terminals, 1

14. A snap switch comprising a switch base, a

pairof ilxed'stops'at least one of which is an electrical contact mounted in said base, a contact bar anchored at one end to said base and having a free end movable between said stops and a thrust seat arranged near said free end and facing the anchored end thereof, spring means for actuating said contact bar, said spring means comprising substantially parallel leaf spring separate compression and tension strips rigidly joined together at one end thereof, the free end of a tension strip being anchored on said base and the free end of a compression strip being stepped in the thrust seat upon said contact bar whereby vertical and longitudinal components of force are applied to said contact bar at the thrust seat. and means responsive to external manipulation for depressing the joined ends of said spring strips to actuate the switch.

15. A'snap switch in accordance with claim 2 wherein at least a portion of said contact bar adjacent the anchored end thereof is flexible in the direction of movement of the free end thereof.

16. A snap switch comprising a switch base, a pair of fixed stops at leastone of which is an electrical contact mounted in said base, an elec trically conductive contact bar anchored at one end to said base and having a free end movable between said stops and a thrust seat arranged 1 near said free end and facing the anchored end thereof, spring means for actuating said contact bar, said spring means comprising substantially parallel leaf spring separate compression and tension strips rigidly joined together at one end thereof, the free end of a tension strip being rigidly mounted in fixed relation to said base and REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,170,748 Eaton Aug. 22, 1939 2,170,767 Riche Aug. 22, 1939 2,197,229 Waddell Apr. 16, 1940 2,204,949 Riche June 18, 1940 2,218,908 Fonseca Oct. 22, 1940 2,228,523 Johnson Jan. 14, 1941 

